
colors.c / colors.h

To convert in-game player name colors to html display.

References used:
    http://www.rapidtables.com/convert/color/hsl-to-rgb.htm
    http://www.rapidtables.com/convert/color/rgb-to-hsl.htm
    https://gitlab.com/xonotic/xonstat/blob/master/xonstat/util.py

Overview:

    This component is slightly based on util.py of XonStats, but the only 
    functionality needed is coloring the player's names. Since C programming 
    language does not have standard libraries for color model conversions and 
    regex, some functionality had to be self written. The function of interest 
    is:
        def html_colors(qstr='', limit=None):

    This component uses purely C standard library.

    Advanced string manipulations such as replace and concatenation are 
    avoided. Instead, strings are printed in parts across functions.

    There is only one instance of dynamic memory allocation. 
        void print_plname(const char *)
    It both allocates, near the start, and frees memory at the end.

darkplaces Player Names & Colors
    Players can add color themes to their names. They're expressed either 
    decimal or hexidecimal.

    The decimal format follows
        A character '^' that is not displayed, followed by a single digit 
        between 0 and 9.
    The hexidecimal format follows
        A string '^x' that is not displayed, followed by 3 digits between 
        0 - 0xF.

Python Regex to C Translation

    The snippets from the original python code:

    _all_colors = re.compile(r'\^(\d|x[\dA-Fa-f]{3})')
    _dec_colors = re.compile(r'\^(\d)')
    _hex_colors = re.compile(r'\^x([\dA-Fa-f])([\dA-Fa-f])([\dA-Fa-f])')

    _dec_spans = [
     "<span style='color:rgb(128,128,128)'>",
     "<span style='color:rgb(255,0,0)'>",
     "<span style='color:rgb(51,255,0)'>",
     "<span style='color:rgb(255,255,0)'>",
     "<span style='color:rgb(51,102,255)'>",
     "<span style='color:rgb(51,255,255)'>",
     "<span style='color:rgb(255,51,102)'>",
     "<span style='color:rgb(255,255,255)'>",
     "<span style='color:rgb(153,153,153)'>",
     "<span style='color:rgb(128,128,128)'>"
    ]

    ...

    def html_colors(qstr='', limit=None):
        ...
        html = _dec_colors.sub(lambda match: _dec_spans[int(match.group(1))], 
                               qstr)
        html = _hex_colors.sub(hex_repl, html)
        ...

    html = _dec_colors.sub(lambda match: _dec_spans[int(match.group(1))], qstr)
        The character following a '^' is treated as an index to the array 
        '_dec_spans'. The corresponding element in '_dec_spans' replaces the 
        character '^' and the following digit in the string 'qstr'.

    html = _hex_colors.sub(hex_repl, html)
        The output of function 'hex_repl' replaces matching strings in html- 
        '^x' followed by 3 hexadecimal digits. The function 'hex_repl' has more
        to do with the algorithms of color model conversions than it has to do 
        with regex rules.

    The control flow to output similar results to the regex substitutions is 
    in the function
        static void b(char * const str);
    Unlike the python counterparts, it segments the player name into tokens and
    prints strings also other strings instead of the sequences not intended to 
    be displayed.

Function Walkthrough
Sorted by caller to callee.

    void print_plname(const char *)
        const char * parameter is the player's name. It is used as a basis for
        the variable 'copy'. 'copy' will always be the shorter character string.

        This is function is intended to be used by the client file.

        This function unconditionally allocates memory (calloc) and frees it at
        the end.

        By itself, it only removes extraneous instances of the character '^'. 
        It then calls the function
            static void b(char * const)
        where actual output occurs.

    static void b(char * const)
        const char * parameter is the player's name. The data pointed at by the
        pointer is altered by function 'strtok', but the pointer itself is 
        never changed. Abstractly, fragments of the player's name are treated 
        as a command to print specific strings.

        This function iterates once through the player's name. 'strtok' 
        segments the player's name; sequences between and not including '^'s 
        are treated as substrings. The first character of the substring is 
        checked for a digit inclusively between 0 and 9 for a decimal color 
        code. Exclusively or, checked for an 'x' and a numerical sequence 
        afterwards for a hexidecimal color code. If the substring does not have
        either, it is printed like an ordinary string.

        This function may not be adequate when a player's name intentionally 
        contains '^'.

    static void hexspan(const char *) 
        const char * parameter is ideally a sequence of 3 hexidecimal digits. 
        Actually it is the entire substring from the callee. The first 3 
        elements are of interest as 3 separate single digit numerical values 
        and are explicitly separated to prevent function 'strtol' from 
        interpreting them as multidigit numbers. These 3 elements are rgb 
        values from the game engine.
        Xonotic represents RGB values as a sequence of three digits 0 - 0xF. 
        Before conversion is to be done, they must be multiplied by 0xF so the
        full range of values for RGB, 0 - 255 can be represented.

        This function prints the an html span tag.

        This function will first convert rgb to hsl to check if the colors are 
        too dark for the web page, and if so brighten up the colors then 
        reconvert to rgb. 

    static void decspan(const int)
        const int parameter is a digit, the range being [0, 9].

        This function is straightforward. It will print an html tag 
        corresponding to the const int parameter.

    void hsl2rgb(struct Rgb *, const struct Hls const *)
        First parameter, 'struct Rgb *' is the result of the conversion. It 
        does not need to be initialized.
        Second parameter, 'const struct Hls const *' is the values and color
        model to convert from and because, it must be initialized.

        The math referenced from:
            http://www.rapidtables.com/convert/color/hsl-to-rgb.htm
        The implemenation deviates at the last 3 lines of code where the 
        results are finalized and placed in the output. The webpage does not
        mention that rounding up is necessary. However it is, otherwise the
        nonzero rgb values for the following colors 
            Silver  (0�,0%,75%)
            Gray    (0�,0%,50%)
            Maroon  (0�,100%,25%)
            Olive   (60�,100%,25%)
            Green   (120�,100%,25%)
            Purple  (300�,100%,25%)
            Teal    (180�,100%,25%)
            Navy    (240�,100%,25%)
        will be off by one.

    void rgb2hsl(struct Hls *, const struct Rgb const *)
        First parameter, 'struct Hls *' is the result of the conversion. It 
        does not need to be initialized.
        Second parameter, 'const struct Rgb const *' is the values and color 
        model to convert from and because, it must be initialized.

        The math referenced from:
            http://www.rapidtables.com/convert/color/rgb-to-hsl.htm
        The implementation deviates when calculating hue, when Cmax is R'. 
        Instead of modulo, there is a summation by 6 when G' is less than B'.
